1. Field of the Invention
The invention relates to an X-ray device, including a C-shaped arm, a first end of which supports an X-ray source and a second end of which supports an X-ray image pick-up device, a carriage which supports the C-shaped arm so that it is pivotable about a pivot axis, and a guide which supports the carriage so that it is tiltable about a tilting axis.
2. Description of Related Art
In such an X-ray device which is known from Japanese patent application JP-2-249533, the C-shaped arm is pivotable relative to the carriage and the carriage is tiltable relative to the guide. The pivot axis and the tilting axis therein extend parallel to one another. Because the carriage is tiltable relative to the guide, the pivoting motion to be performed by the C-shaped arm is greater than if the carriage were rigidly connected to the guide. Before an X-ray exposure can take place, the C-shaped arm and the carriage are locked, using electromagnetic or mechanical locks, in the desired position relative to the carriage and to the guide, respectively. If locking is omitted, the C-shaped arm and/or the carriage will start to pivot or be tilted until the respective mass centers of the C-shaped arm and the carriage are situated in an as low as possible position. Locking is a comparatively time-consuming operation and the electromagnetic or mechanical means required for locking have a comparatively complex and expensive construction. If locking is to be performed manually, there is a risk that the operator forgets to lock the device, so that the C-shaped arm and/or the carriage start to perform an undesirable and possibly risky pivoting and/or tilting motion.
Citation of a reference herein, or throughout this specification, is not to construed as an admission that such reference is prior art to the Applicant""s invention of the invention subsequently claimed.
It is an object of the invention to provide an X-ray device in which the C-shaped arm and the carriage remain in any pivoted and/or tilted position also without being locked.
This object is achieved in the X-ray device according to the invention in that the guide is rotatable about a propeller axis, the tilting axis extending at an angle relative to the propeller axis, a leverage point on the propeller axis being situated near the tilting axis, the mass center of the C-shaped arm being situated on the pivot axis, the mass centers of the C-shaped arm and of the carriage being situated on a leverage line which extends at least substantially through the leverage point, the mass centers of the C-shaped arm and of the carriage being situated to both sides of the leverage point and the ratio of the distance between the mass center of the C-shaped arm and the leverage point to the distance between the mass center of the carriage and the leverage point being substantially equal to the ratio of the mass of the carriage to the mass of the C-shaped arm.
Because the mass center of the C-shaped arm is situated on the pivot axis, the position of the mass center of the C-shaped arm relative to the slide remains constant. Because of the ratios of the distances between the mass centers and the leverage point and the ratios of the masses, the turning moment exerted around the propeller axis by the weight of the C-shaped arm will be compensated in any position by the turning moment exerted around the propeller axis by the weight of the carriage.
Consequently, the C-shaped arm and the carriage need not be locked and can be pivoted and tilted simply by hand. Because locks and drives are not necessary for the C-shaped arm and the carriage, the X-ray device according to the invention may have a comparatively simple, compact and economical construction.
Because of the friction present between the C-shaped arm and the carriage and between the carriage and the guide, the leverage point need not be situated exactly on the leverage line and on the tilting axis. The less friction occurs between the C-shaped arm, the carriage and the guide, the more critical the position of the leverage point and the ratio of the distances and the masses will be.
Therefore, in an embodiment according to the invention the leverage point is situated on the tilting axis and the leverage line. If the ratio of the distances is substantially equal to the ratio of the masses, the C-shaped arm and the carriage will remain in any pivoted and tilted position without locking, even if the friction in X-ray device is comparatively low.